


Monsters in My Head

by Dinocanid



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell, Animal Abuse, Gen, Rated M for language, Reader Is Not Frisk, Spoilers maybe
Language: English
Status: In-Progress
Published: 2016-02-07
Updated: 2017-06-25
Packaged: 2018-05-18 20:22:34
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 13
Words: 9,379
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5941867
Author URL: https://archiveofourown.org/users/Dinocanid/pseuds/Dinocanid
Summary: <blockquote class="userstuff">
              <p>The pup, a little under a year old, wasn't allowed to leave home on her own. She was wanted for reasons unknown to her; but she figured that everyone would eventually forget if she lay low for long enough. Mono couldn’t remember anything from before she lived with Sans. He didn’t seem like the type to just take in strays from the street. Had she done something important? If she did, it was never talked about. Maybe it had something to do with the monsters in her head.</p>
            </blockquote>





	1. Chapter 1

**Author's Note:**

> My first undertale fanfic and second fanfic on AO3. Sans is spelled with a capital S, because this is underfell. This was kind of inspired by Fear The Cute Thing (another underfell fic) but it doesn't share any relations to it.  
> I would appreciate it if anyone was interested in beta-reading future chapters, to help with my writing since it isn't that great.

Mono stared up at the ceiling; tail slowly swishing beneath her. He was away again, that skeleton. His brother always kept him busy with something. The pup, a little under a year old, wasn't allowed to leave home on her own. She was wanted for reasons unknown to her; but she figured that everyone would eventually forget if she lay low for long enough. Mono couldn’t remember anything from before she lived with Sans. He didn’t seem like the type to just take in strays from the street. Had she done something important? If she did, it was never talked about. Maybe it had something to do with the monsters in her head. The ones that spoke to her whenever she was bored or during moments of extreme emotion.

  
“Staring into space will only make time go by slower.”

  
That was Dragonwick. She stated only the facts, or at least what she believed to be true. A bit harsh, but seemed to just want to make the right decisions.

  
“Maybe I’ll take nice stroll in town; enjoy the fresh air.” Mono thought back to herself sarcastically. “I could get killed out there, and you know it. What else do you expect me to do?”

  
“Dragonwick’s right...you shouldn’t just lie there until He comes back.”

  
That was Asha. She disliked sedentary lifestyles and was pretty fond of puzzles, contradicting Mono and Dragonwick, who would rather lie around and hated constant puzzles. (Damn that arrow puzzle in Hotland) If she was ever agreeing with Dragonwick, it must truely mean something important.

  
Mono rolled onto her stomach before standing up. The air felt different since she woke up this...morning? Without a sun, there was no way to truely tell. She just had to trust the clocks and know that AM meant day while PM meant night. They must have wanted her to get up so she could try to find out what caused this feeling. The wolf pup wandered over to the couch and looked out the window. It was mostly boarded up, but she could see through some of the gaps. Nobody was hanging around outside today. Maybe if she snuck out nobody would notice.

  
The front door creaked as Mono slipped outside. Not a monster was in sight, so she kept to the shadows as she moved towards the center of the town.


	2. Chapter 2

The whole town of Snowdin was silent, without a single monster outside. Maybe Tall Skeleton passed through here. Other monsters did tend to stay out of his way, after all. Of course, if he did pass through here then Mono was in huge trouble. She had somehow made her way onto his hit list and had once come way too close to being skewered. The pup considered turning around and heading back to the safety of home, but that feeling was stronger outside and she had to find its source.  
Mono slowly padded through the snow. She had to keep an eye out for Sans as well. He was definitely scary when mad and He would have her head if she was found wandering about on her own. She traveled behind the buildings to stay out of sight and kept her ears perked up. She kept moving until she had left the town and travelled into the forest.

  
“The feeling is even stronger here.” said Asha. “What do you think it is? It feels...empowering.”

  
“Whatever the source is,” Dragonwick replied, “It's probably dangerous so keep quiet, would you? We need to hear.”

  
After a few moments of silent travel, Mono came across a trail of prints on the main trail. Tall Skeleton definitely passed through here, so she steered clear of the main road and kept to the shelter of the trees. Sans was no doubt somewhere around as well. Had they been looking for the source too? The sentry stand that lied ahead was thankfully empty, so perhaps they didn't travel this far. Picking up the pace a bit, Mono trotted past the empty stand and further into the forest. The deeper she went, the less anxious she became about getting caught.  
Eventually, she found a large door at the end of the forest. It was heavy, so she couldn’t push it open. The feeling seemed to peak in this area, but with no way to open the door, she couldn”t progress any further.

  
“Damn it, a dead end.” spat Dragonwick.

  
“Well there’s gotta be a way in or I travelled all this way for nothing!” Mono groaned.

  
“You’ve heard about The Door, haven’t you? It never opens.”

  
The pup rolled her eyes. Of course she didn’t know that, or she wouldn’t have walked all the way to what might as well have been a wall.

  
“Before you say anything else, there's no way we could've known the source would be behind The Door.”

  
Mono huffed and sunk into the snow. Now she would have to make her way all the way back home without Sans knowing she left so He wouldn't kick her-

  
“Mono, the Door!” Asha exclaimed.

  
Mono could feel herself slowly being pushed along with the door as it creaked open. Not wasting any time, she quickly dashed into the nearby foliage to stay out of sight. She looked out from the vegetation and stared back at The Door. Emerging from it was something she'd never seen before. It wore a somewhat torn purple and pink striped sweater and had short hair. It was small and seemed to carry an old boot with a yellow flower planted in it.

  
“I’ve never seen a monster like that before..” said Asha.

  
“That's the source.” Dragonwick stated.

**Notes for the Chapter:**

> Frisk?  
> Frisk.


	3. Chapter 3

“I've never seen a monster like that before.” said Asha.

  
The weird little monster seemed pretty beat up. Nothing too bad, but it was noticeable. There were probably more monsters behind The Door that it probably got in a fight with. After all, it wasn't too uncommon for monsters to be hostile towards one another. The strangest thing was that the little monster appeared to be talking to the flower it was holding. Of course it was probably lonely, but it didn't make it any less strange.  
Before long, the little monster continued on its way into the forest. Mono was hesitant to follow it, but it smelled faintly of dust and could be dangerous. She would have to be able to stop it if it caused any problems.

  
“Monsters kill each other all the time, what’s the big deal?” spat Dragonwick.

  
“I don’t want Sans to be killed.” Mono thought.

  
Mono knew that she couldn't do a good job at protecting anyone, not that Sans even needed it, but she always feared that He wouldn't come home one day and that she would be all alone in a world with deadly monsters. The thought made her shiver. A gate lied up ahead on the path. She had managed to avoid it before by taking the long way around, but the small monster didn’t seem to know about that. Mono stayed hidden in the plants to avoid contact, though it seemed like the small monster wouldn’t be progressing this way.

  
“Mono, do you smell that?” asked Asha.  
Smells like bones and condiments. It was Him.

  
“C-come on, he’s got the small monster. We should go.”

  
Asha insisted that the pup got moving, and she understood the urgency, but Mono listened in. Sans had the small monster trapped with red magic.

  
**“Human.”** He began. **“Don’t you know how to greet a superior?”**

  
Human? That was a human? Mono had heard of humans, but had no idea what one looked like. Humans were responsible for trapping all of the monsters underground and were also targets. If a human Fell Down, then Sans must've been after it’s souI so the monsters can return to the surface.

  
“Mono, come on!” Asha shouted.

  
Mono finally responded and sped away. He had things under control. All she would have to do now was return home.

  
“Was that really a human? Like, from the surface?” Mono thought as she ran home.

  
“Of course it was, didn’t you hear Him?” said Dragonwick.

  
“So, the monsters will be able to return to the surface and kill the humans that trapped underground, right?”

  
Mono hadn’t even been alive long enough to see the surface, unlike other monsters like the king and a few others that are still alive from the war. She heard that it was green and colorful and full of stars at night. Not like those glowing stones in Waterfall, but actual stars. The thought of finally being able to see it made her excited.

  
“You know what this calls for, right?” Dragonwick asked.

  
“Dragonwick, that bar is where the guard dogs hang out!” Asha complained.

  
“So what? It just so happens that we’ve got a dog host.”

  
“Not a dog.” Mono huffed, but she did like the idea of stopping at Grillby's. Sure, it was one of those exclusive fancy-shmancy bars, but the food that Sans brought back from there was great.

  
“The owner's got a soft spot for his lapdogs. As long as we stay on their good side, we can waltz right in.”

  
\---

  
Mono pushed open the door to the bar and stepped inside. It had a dim blue atmosphere and was very spacious. She had only visited this place once before when she accompanied Sans, but now she was on her own and free to have a look around. Music could be heard along with the droning sound of a crowd. The pup wasn’t in any immediate danger here, and she knew that. Everything was much more relaxing and the patrons were also most likely too drunk to do much catching anyway.

**Notes for the Chapter:**

> Thanks for the 2 kudos!


	4. Chapter 4

**Summary for the Chapter:**

> Sorry for the several-weeks wait. Especially for a chapter that's no longer than the other ones.

It turned out well enough. The guard dogs weren't too hostile, and barely payed Mono any attention while the played pool. Or more like chewing on the pool equipment. She wondered if it had to be replaced often, which it probably did. The food she managed to sneak off of some of the tables was good, as always, and she trotted home with a full stomach. It was empty, which means He was still out. Mono made her way up the stairs and curled up in her usual spot by Sans’s door. She prefered to be inside the room, but it was always locked when He wasn’t there. With the house nice, dark, and quiet; Mono yawned and rested her head on the carpet to sleep.

  
\----------

  
*H-Hey! You awake?

  
*...

  
*Oh good, you're awake. We heard you were out for a while. You could've been dead!

  
*...?

  
*Nothing? Are you okay? They won’t listen to me...

  
*I don't think they can speak, or understand for that matter.

  
*Oh... Well, I’ll just have to teach you then! It’s no fun having a buddy who never responds.

  
*Don’t stress yourself. I read the notes, it must remain dumb.

  
*I don’t care what the stupid notes said. How can you ignore a cute face like that?

  
*....

  
*Hey, where are you going??

  
\----------

  
The pup awoke with the sound of a creaking door. She wagged her tail and bounded to the top of the stairs to greet Him, but He was not there. That powerful feeling was back again, and unfamiliar voices could be heard from below. Thoughts connected to each other and Mono realized that it was the human.  
Mono stared at the little human from her sitting-spot at the top of the stairs. Why had this human just wandered into some random home? The canine crept slowly to get a closer look. Her soft paws didn’t make a sound against the carpet. Just a little bit closer and perhaps she could scare it out without-

  
“Frisk, there’s something here!”

  
Shit.

  
Mono had absentmindedly stepped into a ray of what little light was emminating from the mostly covered windows and was spotted. The human stared right at them with the least bit of concern possible. The pup crouched down with her ears flattened against her head when it reached out and ran it’s hand over her head.

  
“It's only another dog.” the human stated  
Mono let out a soft growl. she were not just another “dog”, she were a youthful wolf. she instinctively nipped at the small hand, causing the human to pull back. How did it even get this far in the underworld? It carried no weapon and surely it would’ve been stopped by Him.

  
“It's hurt Him.” said Dragonwick. “How else could it be here? It cannot outrun Him.”

  
Did it really? Mono hadn’t seen Sans since earlier that day, but she had hoped that it was because tall skeleton kept Him busy and not because the human had dusted Him.

  
“What did you do with the skeleton, human?” she growled.

  
“I didn’t do anything to him, I ran away.”

  
“D-don't lie to me! He'd never let a human go.”

  
“We're not lying!” The flower spoke “The bonehead was a wreck when the other one showed up. Frisk managed to slip away.”

  
That much of the news was relieving to hear. Tall skeleton wouldn't kill his brother, or she at least hoped not.

  
“I don't want to hurt anyone,” said the human, “I’m just trying to get home.”

  
“You can’t go through the underworld with hugs and kisses, the king would have your soul before you know what happened to you!”

  
“But you would’ve killed me by now if you really wanted to.”

  
The human turned and walked over to the couch before sitting down; placing the flower on the floor.

  
“Everyone here, they’re my friends. I don’t know what happened to them, but I can’t let everything stay like this.”


	5. Reminisce

**Summary for the Chapter:**

> Sorry for long wait! School is finally out, which means more time for undertale :P  
> Not much of the backstory has been revealed, but it's coming!

“Friends?” Mono questioned. “I don’t know how hard that landing was when you fell down here, but these monsters are not your friends, especially not with a human.”

Frisk shook their head.

“Not now, before! I reset, and everything's dark and corrupted. If I reset now, this world won’t go away. I have to save everyone. Wouldn't you want to save your friends?”

“I don’t have friends, just my owner. Nobody has friends here.” Mono stated. She didn’t understand what the human was talking about, but she did think they were crazy for trying to befriend everyone.

“So I guess Mr. Big Bad “super edgey” Sans decided to adopt a puppy and dress them up in a look-alike shirt and jacket.”

“H-he didn’t give it to me, I found it!”

And it wasn’t because it reminded her of Sans. Absolutely not.

The flower was right, it all sounded as scary as a box of puppies. All of the monsters in the Underworld were murderous...well...monsters. She had seen it with her own eyes. All this talk of worlds and resets made no sense to her. Was there really an alternate world where the monsters were nice? More importantly, were the monsters here really evil?

\-----------

The human, Frisk, left the house after some time. They said that Sans would return soon. How the human would know that was a mystery to her.

 

Mono wagged her tail when Sans came home. He didn't say a word to her and continued towards the couch. When he finally plopped down on the couch, the pup's ears drooped. She could see some new cracks on his skull. Which meant that his brother must have beat him up. Again. Probably for losing the human like she learned earlier. She wished he would stop trying to get his brother’s good graces and stand up to him. He was tough enough for it! But he just refused to do so. Maybe it was a family thing, but she didn’t like it. Instinctively, she hopped up onto the couch and started licking the “wounds”; which he did not take kindly to. The skeleton rolled over and Mono fell to the floor.

“Ack, didn’t I tell ya to keep your tongue away from my face?!” He shouted.

“Sorry...” she whimpered. She stared down at the ground, shuffling her paws. “You really should stop trying to impress your brother though. One of these days he’s going to dust you!”

“What, ya think I don’t know that? I got no choices. Ignore his orders and he kills me. Do what he wants and it isn’t good enough? He still kills me. I’d rather stay right where I am in the middle.”

“Yeah, a kiss up, and how many more cracks is that before you skull breaks in two?” she muttered.

“Mono--” said Asha. The pup didn’t quite catch herself until she was hastily yanked up by the scruff of her neck. Sans glared daggers at her while their faces where a few inches apart. She could swear that his eye lights were gone.

“You mocking me, mutt?” he growled.

“I uh...J-Just want you alive! Hehe...uh..heh?” She stuttered with a nervous grin. God, she needed his pupils to come back. Red glowing orbs were less scary than dark sunken holes any day. She was dropped onto the floor and Sans rolled onto his back again.

“You'd be dead if you said that to anyone else. Remember that, mutt.” he said sternly before leaving it at that.

Mono was going to ask him about what happened after he caught the human, but she was met with the sound of snoring. Typical. He probably wouldn't want to talk about that anyway. What did that flower mean, about him being a wreck? Maybe he was so eager to hand the human to his brother and, along with how nervous he is, the human slipped right past him. Damn. He's trying his best...

She didn't dare jump on the coach again. Not with Sans on it, that is. The pup just settled for resting on the floor beside him. She thought back to the earlier memories of living in the skeleton's home. Anything earlier than that was blank. She remembered how clingy she was. Had much changed? Probably not...

\----*-*-*-----

The house looked very eerie in the dark. There was always the feeling of being watched, and mysterious noises echoed in from outside. A particularly bad snowstorm was going on. Mono always wondered how the weather could get so bad if it was artificial. High winds made the doors creak and occassional hail crashed into the windows. The pup tried to cover her ears, and even hide under the couch, but it was no good. The darkness was still closing in and all the noise didn’t make it any better.

The fear was beginning to get overwhelming, and she broke. Mono dashed up the stairs and rapidly scratched at Sans’s door, yelping and howling. It swung open and she stared up at the tired skeleton with large puppy dog eyes and a wagging tail.

“Can you shut up before you wake the whole town?!” He spat harshly. The pup looked down at her paws.

“...Scared. And dark...” she whined, “I, wanted to stay with you..”

He sighed.

“If I let you inside, will you stop fuckin’ cryin’?

Mono quickly nodded and Sans picked her up by the scruff of her neck. The door closed behind them and she was dropped onto a pile of clothes that was sitting on the floor. Mono yelped from being handled harshly, then found a comfortable spot on the clothes pile to curl up.

\----*-*-*-----

He still allows her to sleep in his room sometimes, but otherwise she just sleeps outside his door. She never was able to climb onto the bed without being kicked back onto the floor. Bones aren’t very comfortable for sleeping anyway.


	6. When he was good...

**Summary for the Chapter:**

> I've actually stopped worrying about the word count per chapter. I know people like to read stories with longer chapters, but whenever I try to do it I just procrastinate and get nothing done. So enjoy somewhat short chapters with more constant updates!

Mono stirred awake when she felt herself being carried. Still half asleep, she shuffled around a bit to stay comfortable as it felt like she was being carried upstairs. A door opened and she dropped to the ground with a thunk.

“OW! What the hell!?” Dragonwick cursed and Mono let out a groan before standing back up on her paws. Apparently, Sans had carried her up to his room. She swore that one of these days he would drop her and she would break something.

“Nice that you’re finally awake, mutt.” said the skeleton.

“I have an name...!” she thought to herself, but no way she was going to actually say that after what happened last night; so she let him continue.

“Here's the deal. Papyrus is on his way over, so you're gonna stay in here and keep your furry ass quiet. Especially none of that damn whinin' you do. Got it?”

The pup nodded and heard a knock on the door downstairs.

“Good girl.” he said before leaving the room and closing the door behind him.

Mono held her ear to the door when Sans let his brother inside. He said no noise, but he didn't say no eavesdropping. Her owner's words were a bit muffled behind the wooden barrier, but she could hear his brother loud and clear.

“I’LL BE HONEST WITH YOU, SANS. MY RECENT ATTEMPTS TO LOCATE THE MONGREL HAVE PROVEN TO BE UNSUCCESSFUL. THE DOCTOR WANTS IT ALIVE OR DEAD, PREFERABLY DEAD, AND I'D RATHER NOT TEST HIS PATIENCE.” said Papyrus.

“N-no problem, boss!”

“GOOD. EVEN YOU SHOULDN’T BE ABLE TO MESS THIS UP. BRING IT TO ME WHEN YOU HAVE FOUND IT. I DON'T WANT ANY EXCUSES THIS TIME.”

A door slammed shut and the house was quiet again.

“Well that was...new.” said Dragonwick.

“Who’s the doctor? I’m not sick, so why does his brother want to take me?” thought Mono as she paced the room.

“I don’t know, but something tells me it’s not for the sniffles. Especially if he wants you alive or dead.” Dragonwick responded.

“W-Will Sans really take us? Papyrus sounded serious, and you know what he does if Sans doesn’t listen...” Asha said with a worried tone.

When was Papyrus not serious? Still, Mono comforted the voice.

“Of course not. He's our owner, he wouldn't do that!” 

Sure, he didn't give her much Tender Loving Care, if at all, but killing her? Could he? Yes. Would he? No...

The door opened again and the pup wagged her tail as a greeting for the skeleton.

“You’ve really turned into a pain, you know that?” Sans said flatly, but she kept on wagging.

“Alright, come on you little bitch,” he said as he picked her up and placed her back in the hallway, “Outside.” The door closed

Mono rolled her eyes at the joke, then turned around and pawed at the door.

“Sans?” she asked.

“What?”

“Who’s the doctor?”

It was quiet for a moment.

“You don’t want to know him.” he finally replied.

Well, she did actually. That's why she asked. Still, that was her cue to not push the subject. When Sans didn't want to talk about it, he didn't talk about it. At least she knew he wasn’t one of those “feel better” doctors. He’s probably like that nutty scientist Alphys that Sans sometimes mentions. Yikes.

**Notes for the Chapter:**

> Edge Pap makes makes an appearance! Although he disappears just as quickly, he'll be back later for a longer time. It sounds like he was ordered to give Mono a "trip" to the doctor..


	7. He was very good

**Summary for the Chapter:**

> Sans takes Mono to Grillby's for lunch and she looks for answers.

**Notes for the Chapter:**

> Contains fluff I guess? It probably doesn't. Special thanks to the users on fanfic amino who helped beta read the previous chapters! (DaisyDogOx, dgreg142)

When Sans woke up from his nap, he told Mono that he was going to Grillby's for lunch; and of course she was going because she hadn't eaten that day. It also meant that he had to carry her there. She had to be kept out of sight during trips, so she was carried in his ribcage and held with his magic to stop her from falling. She didn't really dislike it, but it was the thought of _riding in Sans_ that weirded her out. She was used to it at this point though.

Upon their arrival, he unzipped his jacket and let her out before making his way over to the bar. The stools were too high for the pup, and the skeleton wouldn’t help her, so she hated that she had to jump around like an idiot to pull herself up. Sans always ordered a burger and fries for himself, and he would share it with her if she fetched the mustard from behind the bar. Grillby had stopped giving it to him because he would always drink the whole bottle. While the bartender was busy with other customers, Mono hopped down the other side of the bar, picked up the yellow bottle, and climbed back up. She settled on top of the bar and Sans took the bottle. When the blue (or purple as he seemed to change between the two) fire monster turned back around, he just gave him the look. You know the one where you are just so done.

“That’s my girl.” Sans praised as he pet Mono’s head; all the while giving the bartender the most sly grin ever.

Grillby is sick of your crap, Sans.

He didn't bother to raise a fuss, so he just went back to angrily polishing glasses. Sans ate about half of the food on the plate before sliding the rest to Mono, which she happily gobbled down. Even though he antagonized him, Mono could tell that Sans and Grillby were cool with each other; which proved to be useful. Everyone in the restaurant was of some higher status, so he heard all sorts of important information. Information he probably shouldn’t know. They seem to have an agreement: he keeps Sans’s secrets and Grillby doesn’t “disappear” for knowing too much. Grillby even has the canine unit, which is main unit for snowdin, wrapped around his finger. But then again, they are dogs. All he has to do is feed them and they do whatever he wants.

“I bet he knows why the doctor is looking for you,” said Asha. “Why don’t you ask?”

Looking back, Sans appeared to be taking a nap like he usually did after he ate. She would be able to make her way down the bar and back before he woke up. The pup got down from the bar first, for impression and all that. He probably wouldn’t like it if she walked over the other patrons.

“Um, sir? Sir! Down here???” Mono repeated, but he didn’t respond.

Ok, he was ignoring her. Great. Fantastic.

“I need to know about the doctor!”

“You already do.” he finally said.

Oh.

Wait--

“No. I don't! Sans won't tell me and I guess you won't either.”

“You forgot the doctor, but you know him. So don’t ask me who he is.”

Ok...

“He wants your soul, but that is all I know. Now leave me to my work before you go home with singed fur. I don't appreciate you fetching things from behind the bar.”

Mono didn’t waste any time making her way back over to Sans.

“Heheh, remember the first time you pissed him off? You got a big bald spot right on your--”

“YES, I remember.” She emphasized to cut off Dragonwick. “It took a month to grow back. Please don't mention it again...”

She pawed at Sans to say that she was ready to go home, and he carried her back. He was pleasent today, she wasn’t dropped or kicked around and he even rubbed her belly once! She always loved that. But then he went right back over to the couch. That’s all he ever did; eat and sleep. Unless his brother ordered him around. Mono wished he would get up sometimes. Then she had an idea. Mono playfully nipped at Sans's heel.

"Fight me!" she growled enthusiastically. "I can take a shortstack like you!"

“You don’t want to fight me, mutt. And who you callin’ shortstack? You’re shorter than me.” he said with a lazy chuckle.

“Come on...!” She said as she tugged on his jacket sleeve, her voice was a bit muffled from the fabric in her mouth.

“Fite me!”

“Alright, if it gets you to shut up.”

“Yeah!”

Sans got up and before she could do anything, she was pinned. The hand that held her down was clawed and his teeth were sharp. His jaws opened and snapped shut with an audible.”clink”.

Nope.

“What you starin' for? You said you wanted a fight. Come on tough guy!” He teased with a now sinister looking grin on his face. It was obvious he was trying to scare her, and it was working.

“I, uhh...changed my mind!”

“Is that so?”

“I just ate and I am feeling kind of tired so...”

Sans scoffed and pushed her away before going back to the couch.

“Poser.”

“No I’m not!”

He just took her by surprise, that’s all. She was expecting some sort of playful tussle, but of course reality had to happen. She would remember to just let him sleep next time.

**Notes for the Chapter:**

> Ayyy, this chapter was a bit longer than the last ones! (Almost 3 pages in polaris. I type on my phone so...)


	8. When he was bad...

She said she was tired, but she didn’t sleep.

 

Mono stayed up that night, thinking of things she couldn’t remember. Or, well, not thinking of things she couldn’t remember. She knew the doctor, and he wants her soul, but she forgot. Just like she forgot everything else. That’s why she was wanted, why Papyrus wanted to kill her, and why Sans kept her so hidden. 

 

She was endangering him, yet he refused to change his mind about hiding her in his home. Of all the absurd laws in the underworld, sheltering refugees is recognized as treason. The consequences for which are less than civil.

 

“Sans?”

 

“What?” He grumbled. He sounded groggy.

 

“Am I your friend?” She asked.

 

“You’re a pet.”

 

“Then why do you--”

 

“You found the human didn't you?” Sans said before rolling over to face her. “Don't think that I didn't see your prints in the snow. You led me right to the kid.”

 

“You knew?” The pup said with shock in her voice.

 

“You’re still a dumbass for going out while Papyrus was in town, but you did good. That’s what you’re here for. Now go to sleep.” he said before rolling back over.

 

So if she got killed then he wouldn’t be able to find humans as easily. Mono was disappointed that it didn’t have more depth than that. No one has friends here, she said it herself. That’s the way it had always been; but then why did it suddenly sound bad? 

 

“What if we don't need to find humans anymore? Would I still be a pet?”

 

“...Go to sleep, mutt.”

 

“But y--”

 

“ **I  s a i d** \--” -he sighed- “I said go to sleep...”

 

-

 

The next morning, Mono was...not in the house. She was in what appeared to be a dark room with concrete flooring. There were bars that kept her from the rest of the room; almost like a cell. On the floor was a note left by Sans, so she walked over to read it.

 

*You thought I would let you off that easily for going out? Yeah, no. Don’t do that again. Have fun in solitude, mutt.

P.S: I’m not soulless, I know it gets cold in that shed. Go to the dog house if you start freezing. I don't want to find a pupsicle when I get back.

 

Mono growled. Great, now she was locked in the shed until Sans returned, and who knows when that will be. The shed was cold though. Her jacket could only do so much since it only covered her upper half. Now she wished she actually dressed like the other dogs. Dog pants sounded sooo ridiculous before, and tedious since she wouldn't be able to remove them without help, now she wished she had them.

 

In the corner of the cell was a bowl filled with some dry dog food. It smelled pretty descent, but tasted horrible. How could dogs eat that stuff? Without much else to do, she took shelter inside the dog house; which wasn’t much warmer than the rest of the shed.

**Notes for the Chapter:**

> The next chapter will be longer because I have quite a bit planned for it. I sort of broke this (section?) of chapters into 4 parts so I could keep the name theme going.
> 
> When Sans was good, he was very good. But when he was bad? Well...


	9. He was horrid

Later that day, Mono could hear the creaking sound of the cell being opened. Her ears perked up and she stretched before stepping out of the dog house.

 

“You know, next time you could've just--” she was interrupted when she was snatched up by the neck and she yelped loudly.

 

“YES, THIS IS THE ONE. I HONESTLY DIDN’T THINK YOU COULD DO IT.” said Papyrus.

 

Mono looked around franticly for Sans, who was standing next to the door. She called for help, but he did nothing. If she could cry, she would. The pup had trusted him, and he gave her away to die. She kept barking and whining all the way outside until the taller skeleton closed her muzzle with his hand to shut her up.

 

“You might need to hold her like that all the way to the core, boss. She can be a bit of a crybaby.”

\---

Once they reached the capital, it appeared that they had to pass through a hotel to reach the doctor. The pup could feel that they were getting close and, fearing the worst, she bit down on his arm. No serious damage could be seen, so it probably hurt her own teeth more than it hurt him, but it was enough to make Papyrus drop her and she scrambled away. She ran into one of the back alleys, hid under some of the larger garbage and scraps, and curled up while snapping at the hands. While she was occupied with one, the other grabbed her by the tail and pulled her out. She was lifted up and once again in his arms. Mono whimpered and tried to break free from the skeleton’s clawed grip, but to no avail. He held her tightly, but not too tight.

 

“MY BROTHER WAS RIGHT ABOUT ONE THING. YOU REALLY ARE A “CRYBABY” AREN’T YOU?”

 

The pup's whines didn't stop as she trembled. She was afraid he might snap her neck or strangle her if she didn't get away.

 

But it never came.

 

He continued to pet her and scratch her belly. She could still feel her rapid heartbeat from her panic. Hell, he could just be baiting her for all she knew! But none of that happened.

 

“I’VE DECIDED TO...NOT RETURN YOU TO THE DOCTOR. ONLY TO SHOW HIM THAT HE HAS NO POWER OVER ME! DON’T THINK I’M DOING THIS TO HELP YOU.”

 

 

With that, he placed her back on the ground and Mono looked up at him with a confused expression.

 

“WHAT, YOU DON’T KNOW MERCY WHEN YOU SEE IT? AND THE DOCTOR SAID YOU WERE SUPPOSED TO BE INTELLIGENT...”

 

“It's not that! I just didn't expect you to...nevermind.” said the pup; not wanting to test her luck.

 

He was so adamant about catching her before, and he had finally managed to do so. She wondered what caused him to change his mind so suddenly. Now that she wasn't immediately fearing for her life (she still was, just a little bit), she was able to get a look at him. He loomed over her with his arms crossed and he had a look of impatience. Probably wondering why she hadn't left yet. She couldn’t go home, Sans betrayed her! However, if she couldn't go home then she had nowhere else to go. Then she thought of something.

 

“Uh...is the human and flower still alive?” she asked.

 

“YES. AND?”

 

“If they’re planning on getting out, then I'm going to find them.” Mono said before trotting off.

 

If Sans wasn't going to get her to the surface, then she'll find someone who will.

 

She left the capital and traveled back to Hotland, wanting to get away from the core as fast as possible. The heat was nearly unbearable, especially under her jacket, shirt, and fur. It was fine for Snowdin, which was unnaturally cold, but here it was hell. Quite literally with all the lava everywhere. She had to find the human, and if she sensed it before then she could do it again. The feeling was always faint when it was far away, so she just had to keep walking until it got stronger. 

 

Eventually, it did get stronger. She followed it all the way to the elevators, where the human seemed to be trying to fix them.

 

“Human!” she called while trotting up to them. The flower swiftly turned in surprise, but calmed down when it realized it was only Mono.

 

“I’m going with you to the barrier! You'll need my help anyway, you're just a kid.”

 

“Aren’t we all kids here?” asked Asha.

 

“That’s besides the point.” Mono thought back to herself.

 

“Won't Sans be worried about you? You seemed worried about him when I last saw you.” Frisk said. The pup huffed and looked away.

 

“Sans doesn’t care about me, he never did. I was just a pet he used to find humans. He gave me away so he wouldn’t get in trouble. Human...” she looked back at Frisk. “I just want to get out of this hell. I’m tired of fearing for my life and not being able to trust anyone. You said you wanted to fix everything right? If it gets me out of here, then I want to fix it too.”

 

“It’s okay, you can come with us.”

 

“Just as long as you promise not to get us all in trouble!” the flower added.

 

“I promise.”

**Notes for the Chapter:**

> Mono teams up with Frisk and Flowey to reach the surface! Luckily Papyrus spared her life, but the doctor won't be too happy about that...


	10. The doctor

**Notes for the Chapter:**

> Thanks for the 20 kudos! It might not seem like a lot but for me that's a ton.

Mono stuck close to Frisk when they traveled to the hotel. She asked if there was any other way out, but no. Apparently Frisk already went to the hotel, found out the elevator was broken, and tried to look for a way to fix it. As it stands, going through the Core was inevitable. The pup wished that the underworld wasn’t so linear. When they reached the entrance to the Core, the kid must have caught her trembling because she pet her head to comfort her.

 

“Just stay close, It’ll be fine. The elevator will takes us through it.” they said.

 

Mono was not reassured.

 

\---

 

Mono’s assumptions reigned true because while the human thought they were being productive, the elevator was not working when they arrived.

 

“I don’t get it, Alphys said it was fixed.”

 

“It doesn’t look fixed to me. I knew we couldn’t trust her!” said Flowey.

 

“I’m going to give her a call.” Frisk said as they pulled out their cellphone.

 

There was a moment of silence as Frisk dialed Alphys and talked to her.

 

“The elevator is still off. Huh? Okay, hold on.” the human stopped talking for a moment to walk through the door on the right, only to come back out a few seconds later. “It’s a dead end. No, it's fine. Thanks for trying to help us! Bye.”

 

“Well?” asked Flowey.

 

“Alphys’s ability to manage the core from her lab is being overridden. She can’t help us in here.”

 

“Looks like dingbats wants us to walk.” Flowey replied with an annoyed tone.

 

“It's WingDings.” Frisk chided

 

“Whatever.”

“What? Nonono we are not walking.” Mono argued. “The doctor’s in there and I kind of enjoy being not dead.”

 

“I know you’re scared of him, and so am I, but it’s the only way out. We don’t have any choice but to walk through his trap.”

 

“Fine...”

 

\---

 

After heading down the left hallway, the team was met with a long bridge guarded by lasers. Frisk said that blue meant stop while orange meant go, but that only helped so much when the lasers activated in random orders.

 

The Core was very bright; or at least the main chamber was. Everything below the walkways seemed to get swallowed up by a white glow. Frisk urged the pup to be careful not to fall. The human seemed to know exactly what they were doing and where they were going; including solving the gate puzzle and navigating the maze-like core with ease. To Mono, everything looked pretty much the same, so she was glad that she had a guide.

 

Soon they all crossed the long bridge and were met with another doorway with an elevator next to it, which was still out of order. Frisk walked over to the wall and appeared to touch something in the air before going back to the doorway. Mono stayed close behind as they walked into the dark room up ahead

 

Inside of the room was a figure that the pup found very familiar. He was a skeleton, around Papyrus’s height, with the same outfit that Alphys wore back at the lab. A scientist.

 

“I see that you’ve found my subjects. I've been waiting, and I'll even let you pass freely if you give them to me.” he said.

 

“Gaster, you can't have her. She's going back with me. This world is corrupted and you know it!” said Frisk.

 

“I was being negotiable, but it seems like you want things done the hard way. This world is corrupt because of your own doing, now suddenly you want to fix things? I actually plan to help all of monsterkind.”

 

“By killing her? Why would that help anyone?”

 

“Because, child,” He pointed to the scared wolf pup hiding behing Frisk, “What you have behind you is a milestone in science. The first successful subjects of soul splicing; the act of removing souls and merging them into one.”

**Notes for the Chapter:**

> The plot! It's happening! (And it only took 10 chapters)  
> Also gaster and papyrus have officially joined the story's tags. Now that I've finally revealed a major plotpoint, I can show you the story's cover art!:  
> http://dinocanid.tumblr.com/post/143461346907/the-host-by-hoafan-cover-art  
> (Done by me. HOAFan is my DA account)


	11. Backtracking

 

“We lost the war, but still I was pressured to find a way to tip the odds in our favor. A merged soul is potentially powerful enough to put a boss monster to shame; our soldiers would be unstoppable. Yet, the souls mean nothing if they disappear before they can be retrieved. I must know if they persist after death.”

 

Quick as a flash, three large, floating, dog-like skulls appeared around Gaster. They looked like the ones Mono had seen with Sans once, but spikier and more threatening with their glowing red halos for eyes locked on the gang. Their jaws were curled up into a toothy grin, always smiling. She hated them.

 

“Now, give them to me and you won’t be blasted into oblivion and back. You can leave this world like you always do, and move on to the next one.”

 

“Get ready to move.” Frisk whispered, and Mono looked up at her in agreement.

 

The lasers fired and they dodged. One after the other, they kept on firing; not wanting to let their targets get out alive. They had to get past Gaster and down the hall. The core had no control over the castle’s elevators, so they would work. The team made a dash for the exit, only for a row of bones to shoot out of the ground, blocking their path.

 

A Gaster Blaster hovered over them, charging up another plasma beam and they all braced for impact as the telltale sound of the laser was heard.

 

Seconds later was the sound of the explosion.

 

They opened their eyes when they heard the light sprinkle of dust and shrapnel hitting the ground. The blaster had been reduced to dust, and another one was behind it. It was slightly smaller and had less spikes. It quickly zoomed forward and opened its jaws, scooping the gang up in its mouth. The bones blocking the path to the final hallway were impenetrable, and it flew out the only other exit. Back the way they came. More gaster blasters rammed and blasted the others that attempted to destroy the carrier, and it left the core without serious damage.

 

After fleeing the core, the group landed deep within Hotland. The doctor was no doubt looking for them, but it would take some time for them to be found. The blaster opened its mouth and let them out before hovering again. Sans stood behind them, and with a snap of his fingers the gaster blasters were gone.

 

"You know, kid," he said to Frisk. "I thought you would know not to test your luck by now. Did you really think you could get past Gaster without an ounce of power?"

 

"Well...It worked with everyone else didn't it?" Frisk asked.

 

"Gaster isn't like everyone else. If he hit you once, you would've been done."

 

“But that's the only way out! We're gonna have to go back sooner or later to stop him.”

 

“After that stunt I pulled to get you brats outta there? No way. Go back there now and he'll jump you at the door. If you want to stop him you’ll have to destroy his research. I’m guessing he told you, he always was one to _mono_ logue.” He said before looking at Mono, who growled and looked away.

 

“What, you didn’t like that? Alright, fine, we've got life threatening problems to solve or whatever.” Sans turned and began walking off in the opposite direction. “You know the way to the lab, no need for me to guide you.”

 

“Wait!” Mono shouted after him. “Why are you helping us? Why do you care?”

 

“Frisk and Gaster aren't the only ones who know the world's corrupted.” Then he was gone.

 

\---

 

The gang made their way to Alphys' s lab. After Frisk waved at the camera outside, the doors opened and they walked in. Alphys scooted back from the desk full of papers and approached them. She looked apologetic.

 

“I really am sorry I couldn’t get you out Frisk! I just want this all to be over...” she said.

 

“I know, you don't have to be sorry. But we do need your help finding where Gaster keeps the documents from the soul splicing research in the lower lab. We have to get rid of them.”

 

“D-Down there? Are you sure? What if he comes back and finds us poking around? I can only imagine what he’ll do to me if he finds out that I’m helping you guys.”

 

“You know where it is though, right? We could hurry and come straight back!”

 

“Oh fine, but you have to be quick about it!”

 

Everyone entered the elevator and Alphys pressed the button to go down. There was a long silence until the doors opened up again and they stepped out.

 

The lab looked pretty new, a sign of its limited use, with many branching hallways. If it didn't smell like old guts and dust it would've been nice to look at.

 

“It’s all the way down the first hall and you make a left. In the room is a door with a keypad; the key is 7891. Try not to get lost! I’ll call you if I hear anything.”

 

\---

 

The room they entered was full of metal cages on shelves; all of which were empty. They must have been used to hold the subjects.

 

Just like Alphys said, there was a door in the room and the code that Frisk entered made it open with a *click*. It looked like an office, with a desk and several file cabinets. The cabinets and the folders inside were alphabetically ordered. Under “S” were all the notes Gaster had taken...and Frisk couldn’t read them.

 

“Uh, it’s in WingDings.” they said.

 

Mono hopped onto the desk to get a better view, and the writing actually made sense.

 

“I can read it, try to get a closer look.” said Dragonwick.

 

The pup nodded and asked Frisk if she could get a closer look at the notes. They placed the notes on the table for her to read and sat in the chair behind her.

 

“Can you read it out loud?” They asked and Mono agreed.

 

-Day 1-

The Canine Unit fetched me another subject today. It appears a juvenile of the species Canis Lupus or, in layman's terms, a wolf pup. I am impressed that nothing was broken from the fall, but it is in a poor state. Unhealthy subjects are useless for testing, but this one is resilient. It will be treated and stored with the other subjects once healed.

 

-Day 4-

After 3 days, the subject seems to be back to normal. Simple observational tests have taught that it has a purple soul. Perseverance, almost like a cousin to determination. That would explain it's ability to remain so strong. I have scheduled to begin testing tomorrow.

 

-Day 6-

The new subject appears to get along well with the older subjects. This is good, because they'll be inseparable. I am confident it will work this time.

 

-Day 7-

The procedure was a success. The subject's vitals are proper and the soul is operating as normal. Without a soul, the other subjects have reduced to dust, as predicted.

 

-Day 9-

The canine subject has gained intelligence. I believe it is a result of the magic in a monster's soul. How much more powerful is conjoined magic?

 

-Day 10-

In order to test the subject's magical durability, it was exposed to high amounts of magic. The results were...interesting. The subject had changed. It grew horns and spikes, and the fur on its muzzle, paws, and tail had receded in order to be replaced with scales, clawed fingers and feet, and a thicker tail. The previous subjects were still present.

 

-Day 11-

It is now proven that soul splicing results in much higher ATK. But now that the notes have been recorded, the tests can be successfully replicated. Only one test remains; does the soul persist after death? If it does, they can be retrieved on the battlefield and used to make stronger monsters. Those humans would be digging a grave for themselves.

 

-Day 12-

The subject is gone. It knew that its fate was not far away. I have ordered the royal guard to retrieve it alive or kill it and bring me the soul if it doesn't disappear shortly after death. They are incompetent, but should be more than capable of capturing an animal.

**Notes for the Chapter:**

> Fun fact: I actually wanted to add this chapter before I left for Otakon but uh...that didn't happen. On the bright side, I got to be Frisk for a weekend, carry flowey, and ran into the lord of hyperdeath twice. I didn't make any photoshoots though.
> 
> I stayed up until 6AM finishing this for you guys x.x  
> Is it just me or is it that when writing I feel like I'm doing both too much and too little at the exact same time.


	12. Poll time!

Not a chapter, but a poll! I've been split on whether I want the next chapter to be a flashback chapter or if I want to continue in the present. As a reward for sticking with this story, the readers get to decide! All you have to do is comment either flashback or continue and I'll see what gets the most votes! ~~(Assuming anyone actually enters.)~~


	13. The only way out is forward

**Summary for the Chapter:**

> In which the gang rents a hotel and Sans spills some exposition.

**Notes for the Chapter:**

> I live! This was on hiatus even longer than Beginnings. Now that it's summer vacation I can actually commit time to my hobbies. The battle scene that was giving me so much trouble will not be in this chapter. Sorry if it's not very good.

She was nothing more than a vessel; a test to see if stray souls on the battlefield could make the soldiers stronger. Mono had no idea how to take it, and Dragonwick and Asha were just as surprised. It was already horrible being in a body they can feel yet not control, but they were “dead”. Memories returned in bits and pieces, but the whole story was still lost. They remember escaping, but that was it. Anything before was still gone .

Was Sans protecting her then? It almost made her feel bad for hating him now. Almost. She had to focus on the now; and right now the papers had to be destroyed. The documents were shredded to unreadable pieces after a few bites.

“This doesn't solve our problem!” Flowey piped up. “As far as we know, that bag of bones is still guarding the exit!”

“It doesn't fix it, but it stops things from getting worse.” Frisk replied. “The only way out is forward, we just have to get past him.”

“And how well did that turn out for us?”

“We'll just have to defeat him” Mono intervened.

“Go ahead and try. You know how much LV he's got?” Sans said as he appeared from…somewhere. “It's out of this world, mutt. You're not even a monster and he'll dust ya.”

Could Gaster be that powerful for real? He was scary, sure, but he couldn't be any stronger than the king…right?

“You act like that doctor's some sort of god! There has to be some way to kick his sacrum.” Mono exclaimed in disbelief.

“From what I've seen, he probably is.” Frisk said. “If we defeat him he'll always be…somewhere else.”

So immortal demon skeleton just…exists? _Perpetually??_ Well that’s just…fantastic. What now? The only way out is forward. Mono was filled with, perseverance? It felt terrible actually. Knowing that you have to move on but the solution seems impossible.

Just then, Frisk’s phone began to ring. The only thing the pup was thinking now was “oh crap”, but it turned out to be a false alarm.

“You said you would call if it was an emergency! I was kind of freaked out. Okay, we're coming back.” They hung up. Alphys told them that staying too long was a really bad idea, so everyone agreed that it was time to go.

“We could stay at the hotel for the night.”

“That's literally right next to the core!”

“Gaster wouldn't bother looking for us now, he knows we'll be back.”

* * *

 

The hotel room had a small space with a couch and a television. On the other side of the room was a door to the bedroom. It contained a bed and a shelf, but nothing else.

 

“Go ahead and take the room, kid. I'll stick to the couch.”

Mono followed Frisk into the bedroom and watched them place Flowey on the shelf. Then they picked up Mono and placed her on the bed.

“You should get some sleep. I know you're tired after all that's happened.”

“R-Really?”

“Why not?”

“I’ve uh, never slept in a bed before. Thank you human!”

“You can call me Frisk you know.”

“Well, thanks Frisk. Aren't you sleeping too?”

“I wanted to talk to Sans about something. I'll just be a minute.”

Frisk left the room and Mono took the opportunity to marvel at the bed. She felt the sheets under her paws, rolled around on the mattress and crawled around under the covers.

“This is much more comfortable than the floor! Sans would never let me sleep in his bed, and the other room was always locked. I snuck in once, but he just rolled over me. Did you know he's heavy? I know it's like ghost fat or whatever but he's really heavy. Am I that round? I think only eating cheeseburgers and fries will do that to you-“

“We'll never get any sleep with your yapping!”

“...sorry…”

She sat quietly on the bed, but couldn't get to sleep. Her mind was still racing.”

“You know what perseverance feels like?”

Flowey groaned. He felt defeated now.

“No, but I feel like you're about to tell me anyway.”

“It's like you have to do something and you know it will be terrible. Like you can just feel that it's going to suck but…there's no way to avoid it. You just have to take the pain and hope it doesn't kill you. The ends justify the means”

“That's…stupid.”

“I know, right?”

….

“I'm getting all sentimental aren't I?”

“Yes.”

“Uuugh…I hate this…”

“Just go to sleep before you tell me some weird embarrassing shit.”

“I'll do that.”

The pup circled around before curling up on the bed. She blinked a few times and layed there in silence for some time, but she couldn't fall asleep.

“Hey, Flowey?”

“What??”

“There was this one time I drank from some random bottle behind Grillby’s counter—“

“Aaaagh! _No!_ Go to sleep!”

* * *

 

“You never answered her question.”

“What're you talking about, kid?”

“Why you took care of her.”

They heard Sans sigh after saying that.

“You really want to know, don't you?”

Frisk nodded and sat at the foot of the couch patiently. His expression was unreadable; but he knew that they would pry for an answer; an answer he was tired of keeping.

“Mono's friends, you know,” he tapped his skull “I used to know them, two sisters; they weren't bad kids. One day their parents were killed and they holed themselves up in the house like nobody lived there. The doc had all of the vulnerable monsters snatched up, and they knew he was coming for them. I came by now and then to make sure they weren't starving; but one day they were just…gone. He got wise and picked 'em up himself. I couldn't do anything to get them out.”

Sans was staring at the ground now, filled with guilt. 

“You read the notes, you know what went down after that. Not only weak or injured monsters, but kids with nobody to look after ‘em would just...disappear. Don't get me wrong, I wanted revenge on the surface too, but somewhere you have to draw the line. When I found that mutt washed up by the river after she escaped, I knew it was still them, even if they couldn’t remember me.”

 “Kid, listen, don't tell her all that sappy stuff, okay? I don't need her getting attached to me again, especially now.”

 

 

**Notes for the Chapter:**

> The next chapter will be a short little flashback/lore chapter to tide you over until I can get the next one done.


End file.
